Reactive species, such as halogen species and halogen-containing compounds are used extensively in the microelectronics industry to dry etch silicon and other semiconductors. In dry etching, a substrate is exposed to reactive gases, ion beams or plasmas to remove material from the surface of the substrate. Halogen species and halogen-containing compounds are used as dry etchants because they react with many semiconductor materials to produce volatile products that are efficiently removed in a vacuum. Halogen species are often provided using plasma sources.
Unfortunately, dry etching often roughens the surface of a substrate, leading to defects, both physical and electronic, that affect performance of microelectronic devices. Roughening of a semiconductor surface during dry etching, especially during plasma etching, is understandable, as the multiple reactive species typically used react with the semiconductor surface at different rates. Even if a single reactive species were involved in such an etching process, a distribution of energies and trajectories can lead to differential etching rates across a substrate surface causing surface defects. Thus, many defects that arise during dry etching are a result of the inhomogeneity of the etchant itself. As microelectronic devices continue to shrink in size, even small defects that arise from the etching process become less tolerable, making well-characterized and controllable sources of reactive species desirable.
Emission of neutral halogen atoms from solid alkali halides may be stimulated using electron, ion and photon beams. Two types of emission are typically observed in these processes: emission of halogen atoms with a distribution of near-thermal energies and emission of halogen atoms having a distribution of hyperthermal energies. What has not been appreciated is that selective photo-excitation may provide control over the kinetic energy of hyperthermally emitted neutral halogen atoms and that hyperthermal emission from halide surfaces occurs with a narrow distribution of trajectories. These surprising discoveries, in part, make possible the presently disclosed solid state halogen sources.